It’s hard to know, because data isn’t collected on a national level. According to the Council for Responsible Genetics, the number of babies born to gestational surrogates almost doubled from 2004 to 2008, from 738 babies to nearly 1,400.

How do surrogate pregnancies work?

There are two types of surrogacy -- traditional surrogacy and gestational surrogacy. In traditional surrogacy, the surrogate mother’s egg is artificially inseminated and she carries the pregnancy to term. The child is genetically related to the surrogate mother, because her egg was used.

In gestational surrogacy, a woman uses her own egg, which is fertilized by either her partner or a sperm donor. The embryo is then transferred to the surrogate mother who carries the pregnancy to term. The child is not genetically related to the surrogate mother, because her egg was not used.

How much does the surrogate process cost?

Some surrogate mothers choose to carry a pregnancy for free. Others charge from $12,000 to $25,000, according to the Council for Responsible Genetics.

Is surrogacy dangerous?

Few studied have looked at the safety of surrogacy. But the health impact of fertility treatments and pregnancy can be serious, and deaths of surrogate mothers have been reported. One recent death involved an Idaho woman who was acting as a surrogate for a couple in Spain. The 34-year-old woman died while pregnant with twins.

Is surrogacy ethical?

“In many ways, [the McKissacks’ case in Plano] is a better surrogacy arrangement than some of the other surrogacy arrangements we see taking place worldwide,” said Josephine Johnston, a research scholar at The Hastings Center in New York. Among the advantages of the McKissacks’ case: The surrogate mother and baby received quality medical care; the surrogacy was voluntary rather than for-hire; the baby is biologically related to both parents; and the parties have a strong bond, which reduces the risk of postpartum acrimony.

Dr. Seema Yasmin, a physician and former CDC epidemiologist, is a professor at the University of Texas at Dallas.